Method and systems for shading and shadowing volume-rendered images based on a viewing direction

ABSTRACT

Various methods and systems are provided for generating a volume-rendered image with shading from a three-dimensional ultrasound dataset. As one example, a method for ultrasound imaging includes generating a volume-rendered image with shading and shadowing from a three-dimensional ultrasound dataset, the shading and shadowing based on an angle between a probe axis of a transducer probe used to acquire the three-dimensional ultrasound dataset and a viewing direction of the volume-rendered image.

FIELD

Embodiments of the subject matter disclosed herein relate to methods andsystems for shading and shadowing volume-rendered images.

BACKGROUND

Volume-rendered images may be useful for representing 3D medical imagingdatasets. There are currently many different techniques for generating avolume-rendered image. One such technique, ray-casting, includestraversing a number of rays through the 3D medical imaging dataset. Eachvolume sample (e.g., voxel) encountered during ray casting is mapped toa color and a transparency value. According to one approach, the colorand opacity values are accumulated along each ray using front-to-back orback-to-front volume composition and the accumulated color value isdisplayed as a pixel in the volume-rendered image. In order to gain anadditional sense of the orientation of surfaces within the volumetricdata, volume-rendered images may be shaded using gradient shadingtechniques. Gradient shading techniques compute reflections based onimplicitly defined surface normals computed from volume gradientsrelative to a pre-defined light direction. Both diffuse and specularreflections are taken into account in the gradient shadedvolume-rendered image. Other shading methods, such as methods based oncomputing gradients from a depth buffer may be used instead of gradientshading. Furthermore, volumetric shadowing techniques can be used toenhance perception of depth as well as shapes of structures within thevolumetric data. Volumetric shadowing techniques take a predefined lightdirection or pre-defined light source position into account forcomputing the shadows. Various methods for shading and volumetricshadowing (hereafter simply referred to as shadowing) are known to thoseskilled in the art. The shading and shadowing help a viewer to moreeasily visualize the three-dimensional shape of the object representedby the volume-rendered image.

Some ultrasound imaging systems typically allow the user to controlrotation of the volume-rendered image in order to change a viewingdirection of the image. However, the resolution of the volume-renderedimage may be anisotropic, for example, when the ultrasound image isacquired at fundamental frequencies. As such, the image resolutionchanges from a radial direction (e.g., a direction normal to thetransducer probe surface and in a direction of a probe axis of thetransducer probe) to a lateral (e.g., a direction perpendicular to thetransducer probe surface normal, also referred to herein as a side view)and elevation direction. For example, when ultrasound data is viewedfrom the lateral direction, the resulting volume-rendered image has amore noisy and unstable appearance than when the ultrasound data isviewed from the radial direction. Many of the shadows and reflectionscreated in the lateral view volume-rendered image may not correspond toreal structures, thereby degrading the ability of the user to make anaccurate medical diagnosis. These issues have been recognized by theinventors herein, and are not admitted to be generally known.

BRIEF DESCRIPTION

In one embodiment, a method for ultrasound imaging comprises generatinga volume-rendered image with shading and shadowing from athree-dimensional ultrasound dataset, the shading and shadowing based onan angle between a probe axis of a transducer probe used to acquire thethree-dimensional ultrasound dataset and a viewing direction of thevolume-rendered image.

It should be understood that the brief description above is provided tointroduce in simplified form a selection of concepts that are furtherdescribed in the detailed description. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined uniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 is a schematic diagram of an ultrasound imaging system accordingto an embodiment.

FIG. 2 is a schematic representation of a geometry that may be used togenerate a volume-rendered image according to an embodiment.

FIG. 3 is a schematic representation of different viewing directions ofa volume-rendered image according to an embodiment.

FIG. 4 is a flow chart of a method for generating a volume-renderedimage based on a viewing direction according to an embodiment.

DETAILED DESCRIPTION

The following description relates to various embodiments of generating avolume-rendering image with viewing angle-dependent shading andshadowing. An ultrasound imaging system, such as the system shown inFIG. 1 may be used to acquire three-dimensional ultrasound data via atransducer probe. A processor of the ultrasound imaging system mayaccess the three-dimensional ultrasound data and use various techniques,such as the example technique depicted in FIG. 2, to generate avolume-rendered image from the three-dimensional ultrasound data.Shading and shadowing may be used to enhance the volume rendered image.For example, shading and shadowing may be determined based on one ormore shading and shadowing parameters such as a light source position,light source strength, and light attenuation. However, due to the natureof the ultrasound data (e.g., due to the anisotropic nature of theultrasound imaging system), the volume resolution of the volume-renderedimage is anisotropic. Thus, when the volume-rendered image is viewedfrom different viewing directions relative to a probe axis of thetransducer probe, as shown in FIG. 3, the appearance of the renderedimage changes. For example, as an angle between the probe axis and theviewing direction increases, the rendered image may become degraded.Thus, a method, such as the method shown in FIG. 4, may includeadjusting the one or more volume-rendering shading and shadowingparameters based on the angle between the probe axis and the viewingdirection.

Before further discussion of the approach for generating thevolume-rendered image with viewing angle dependent shading andshadowing, an example ultrasound imaging system that may be used toacquire three-dimensional ultrasound data is shown in FIG. 1.Specifically, FIG. 1 is a schematic diagram of an ultrasound imagingsystem 100 in accordance with an embodiment. The ultrasound imagingsystem 100 includes a transmitter 102 that transmits a signal to atransmit beam former 103 which in turn drives transducer elements 104within a transducer array 106 to emit pulsed ultrasonic signals into astructure, such as a patient (not shown). A probe 105 includes thetransducer array 106, the transducer elements 104 and probe/SAPelectronics 107. The probe 105 may be an electronic 4D (E4D) probe, amechanical 3D probe, or any other type of probe capable of acquiringthree-dimensional ultrasound data. The probe/SAP electronics 107 may beused to control the switching of the transducer elements 104. Theprobe/SAP electronics 107 may also be used to group the transducerelements 104 into one or more sub-apertures. A variety of geometries oftransducer arrays may be used. The pulsed ultrasonic signals areback-scattered from structures in the body, like blood cells or musculartissue, to produce echoes that return to the transducer elements 104.The echoes are converted into electrical signals, or ultrasound data, bythe transducer elements 104 and the electrical signals are received by areceiver 108. The electrical signals representing the received echoesare passed through a receive beam-former 110 that outputs ultrasounddata or three-dimensional ultrasound data. A user interface 115 may beused to control operation of the ultrasound imaging system 100,including, to control the input of patient data, to change a scanning ordisplay parameter, and the like.

The ultrasound imaging system 100 also includes a processor 116 toprocess the ultrasound data and generate frames or images for display ona display device 118. The processor 116 may include one or more separateprocessing components. For example, the processor 116 may include acentral processing unit (CPU), a microprocessor, a graphics processingunit (GPU), or any other electronic component capable of processinginputted data according to specific logical instructions. Having aprocessor that includes a GPU may advantageous for computation-intensiveoperations, such as volume-rendering, which will be described in moredetail hereinafter. The processor 116 is in electronic communicationwith the probe 105, the display device 118, and the user interface 115.The processor 116 may be hard-wired to the probe 105 and the displaydevice 118, and the user interface 115, or the processor 116 may be inelectronic communication through other techniques including wirelesscommunication. The display device 118 may be a flat panel LED displayaccording to an embodiment. The display device 118 may include a screen,a monitor, a projector, a flat panel LED, or a flat panel LCD accordingto other embodiments.

The processor 116 may be adapted to perform one or more processingoperations according to a plurality of selectable ultrasound modalitieson the ultrasound data. Other embodiments may use multiple processors toperform various processing tasks. The processor 116 may also be adaptedto control the acquisition of ultrasound data with the probe 105. Theultrasound data may be processed in real-time during a scanning sessionas the echo signals are received. For purposes of this disclosure, theterm “real-time” is defined to include a process performed with nointentional lag or delay. An embodiment may update the displayedultrasound image at a rate of more than 20 times per second. The imagesmay be displayed as part of a live image. For purposes of thisdisclosure, the term “live image” is defined to include a dynamic imagethat is updated as additional frames of ultrasound data are acquired.For example, ultrasound data may be acquired even as images are beinggenerated based on previously acquired data and while a live image isbeing displayed. Then, according to an embodiment, as additionalultrasound data are acquired, additional frames or images generated frommore-recently acquired ultrasound data are sequentially displayed.Additionally or alternatively, the ultrasound data may be storedtemporarily in a buffer during a scanning session and processed in lessthan real-time in a live or off-line operation. Other embodiments of theinvention may include multiple processors (not shown) to handle theprocessing tasks. For example, a first processor may be utilized todemodulate and decimate the ultrasound signal while a second processormay be used to further process the data prior to displaying an image. Itshould be appreciated that other embodiments may use a differentarrangement of processors.

The processor 116 may be used to generate an image, such as avolume-rendered image or a planar image, from a three-dimensionalultrasound data acquired by the probe 105. According to an embodiment,the three-dimensional ultrasound data includes a plurality of voxels, orvolume elements. Each of the voxels is assigned a value or intensitybased on the acoustic properties of the tissue corresponding to aparticular voxel.

Still referring to FIG. 1, the ultrasound imaging system 100 maycontinuously acquire ultrasound data at a frame rate of, for example, 5Hz to 50 Hz depending on the size and spatial resolution of theultrasound data. However, other embodiments may acquire ultrasound dataat a different rate. A memory 120 is included for storing processedframes of acquired ultrasound data that are not scheduled to bedisplayed immediately. The frames of ultrasound data are stored in amanner to facilitate retrieval thereof according to the order or time ofacquisition. As described hereinabove, the ultrasound data may beretrieved during the generation and display of a live image. The memory120 may include any known data storage medium for storing data,including, but not limited to a hard drive, a flash memory, randomaccess memory (RAM), read only memory (ROM), a compact disc (CD), and acompact disc read-only memory (CD-ROM). The memory 120 may be part of adatabase, a component of a PACS/RIS system, or a stand-alone component.The processor 116 is communicatively connected to the memory 120. Thismay be via either a wired or a wireless connection.

Optionally, embodiments of the present invention may be implementedutilizing contrast agents. Contrast imaging generates enhanced images ofanatomical structures and blood flow in a body when using ultrasoundcontrast agents including microbubbles. After acquiring ultrasound datawhile using a contrast agent, the image analysis includes separatingharmonic and linear components, enhancing the harmonic component andgenerating an ultrasound image by utilizing the enhanced harmoniccomponent. Separation of harmonic components from the received signalsis performed using suitable filters. The use of contrast agents forultrasound imaging is well known by those skilled in the art and willtherefore not be described in further detail.

In various embodiments of the present invention, ultrasound data may beprocessed by other or different mode-related modules. The images arestored and timing information indicating a time at which the image wasacquired in memory may be recorded with each image. The modules mayinclude, for example, a scan conversion module to perform scanconversion operations to convert the image frames from Polar toCartesian coordinates. A video processor module may be provided thatreads the images from a memory and displays the image in real time whilea procedure is being carried out on a patient. A video processor modulemay store the image in an image memory, from which the images are readand displayed. The ultrasound imaging system 100 shown may be a consolesystem, a cart-based system, or a portable system, such as a hand-heldor laptop-style system according to various embodiments.

FIG. 2 is a schematic representation of geometry that may be used togenerate a volume-rendered image according to an embodiment. FIG. 2includes a 3D medical imaging dataset 150 and a view plane 154.

Referring to both FIGS. 1 and 2, the processor 116 may generate avolume-rendered image according to a number of different techniques.According to an exemplary embodiment, the processor 116 may generate avolume-rendered image through a ray-casting technique from the viewplane 154. The processor 116 may cast a plurality of parallel rays fromthe view plane 154 through the 3D medical imaging dataset 150. FIG. 2shows a first ray 156, a second ray 158, a third ray 160, and a fourthray 162 bounding the view plane 154. It should be appreciated thatadditional rays may be cast in order to assign values to all of thepixels 163 within the view plane 154. The 3D medical imaging dataset 150may comprise voxel data, where each voxel, or volume-element, isassigned a value or intensity. Additionally, each voxel may be assignedan opacity as well. The value or intensity may be mapped to a coloraccording to some embodiments. The processor 116 may use a“front-to-back” or a “back-to-front” technique for volume composition inorder to assign a value to each pixel in the view plane 154 that isintersected by the ray. For example, starting at the front, that is thedirection from which the image is viewed, the intensities of all thevoxels along the corresponding ray may be summed. An opacity value,which corresponds to light attenuation, is assigned to each voxel. Theintensity is multiplied by the opacity of the voxels along the ray togenerate an opacity-weighted value. These opacity-weighted values arethen accumulated in a front-to-back or in a back-to-front directionalong each of the rays. The process of accumulating values is repeatedfor each of the pixels 163 in the view plane 154 in order to generate avolume-rendered image. According to an embodiment, the pixel values fromthe view plane 154 may be displayed as the volume-rendered image. Thevolume-rendering algorithm may additionally be configured to use anopacity function providing a gradual transition from opacities of zero(completely transparent) to 1.0 (completely opaque). Thevolume-rendering algorithm may account for the opacities of the voxelsalong each of the rays when assigning a value to each of the pixels 163in the view plane 154. For example, voxels with opacities close to 1.0will block most of the contributions from voxels further along the ray,while voxels with opacities closer to zero will allow most of thecontributions from voxels further along the ray. Additionally, whenvisualizing a surface, a thresholding operation may be performed wherethe opacities of voxels are reassigned based on the values. According toan exemplary thresholding operation, the opacities of voxels with valuesabove the threshold may be set to 1.0 while voxels with the opacities ofvoxels with values below the threshold may be set to zero. Other typesof thresholding schemes may also be used. An opacity function may beused to assign opacities other than zero and 1.0 to the voxels withvalues that are close to the threshold in a transition zone. Thistransition zone may be used to reduce artifacts that may occur whenusing a simple binary thresholding algorithm. For example, a linearfunction mapping opacities to values may be used to assign opacities tovoxels with values in the transition zone. Other types of functions thatprogress from zero to 1.0 may also be used. Volume-rendering techniquesother than the ones described above may also be used in order togenerate a volume-rendered image from a 3D medical imaging dataset.

The volume-rendered image may be shaded in order to present the userwith a better perception of surface orientation. This may be performedin several different ways according to various embodiments. For example,a plurality of surfaces may be implicitly defined based on thevolume-rendering of the 3D medical imaging dataset. According to anexemplary embodiment, a gradient may be calculated at each of thevoxels. The processor 116 (shown in FIG. 1) may compute the amount oflight at positions corresponding to each of the voxels and applystandard shading methods based on the gradients and specific lightdirections, as well as other parameters such as light strength,attenuation and reflectivity. The shading process may incorporate bothspecular and diffuse reflections to brighten image details. The specularand diffuse reflections simulate light reflections from the light sourcehitting the surfaces and bouncing back toward the viewer. Thus, thespecular and diffuse reflections included in the volume renderingalgorithm depend on the light direction, the local surface orientation(e.g., gradient normal), and the viewing direction used to create thevolume-rendered image (the viewing direction will be described furtherbelow with reference to FIG. 3). In this way, the volume-rendered imagemay be shaded based on one or more volume-rendering shading parameters.

Generating the volume rendered image may further include applyingshadowing effects to the image. Shadowing of volume rendered images maybe performed according to different shadowing methods. Various types oflighting may be used in the shadowing process: direct lighting to createsharp shadows via monochromatic light attenuation, indirect lighting tocreate soft shadows via diffuse chromatic light attenuation, and/orambient lighting to lighten dark portions of the image. The indirectlighting simulates light scattering effects, thereby creating softcolored shadows. Thus, in one example, the volume rendered image mayinclude a combination of direct, indirect, and ambient lighting.

According to one exemplary embodiment, the 3D data set may be slicedwith multiple planes orthogonal to half of an angle between the lightdirection and the viewing direction. Light intensity on each slicedplane is calculated based on the light intensity on a previous slicedplane and the opacity of each sample on the previous sliced plane. Thecalculated light intensity can then be applied to the voxels duringvolume composition for creating the shadowing effects. Thus, thisexemplary method, or another possible shadowing method, may create oneor more volume-rendering shadowing parameters for shadowing thevolume-rendered image.

Further, as introduced above, the shadows and light reflections of thevolume-rendered image may change based on a direction of the lightsource applied to the volume-rendered image.

The view direction may correspond with the view direction shown in FIG.2. The processor 116 may also use multiple light sources as inputs whengenerating the volume-rendered image. For example, when ray casting, theprocessor 116 may calculate how much light is reflected, scattered, ortransmitted from each voxel in a particular view direction along eachray. This may involve summing contributions from multiple light sources.The processor 116 may calculate the contributions from all the voxels inthe volume. The processor 116 may then composite values from all of thevoxels, or interpolated values from neighboring voxels, in order tocompute the final value of the displayed pixel on the image. While theaforementioned example described an embodiment where the voxel valuesare integrated along rays, volume-rendered images may also be calculatedaccording to other techniques such as using the highest value along eachray, using an average value along each ray, or using any othervolume-rendering technique.

FIG. 3 is a schematic representation of a volume-rendered image anddifferent viewing directions of the volume-rendered image relative to aprobe axis. Specifically, schematic 300 of FIG. 3 shows a geometricalrepresentation of a volume-rendered image 302 and the relativepositioning of a probe axis 304 of a transducer probe 306 used toacquire the 3D ultrasound data represented by the volume-rendered image302. As one example, as shown in FIG. 3, the probe axis 304 is thecentral axis of the transducer probe which is positioned normal to aplane tangent to a surface formed by the transducer elements of thetransducer probe 304. Thus, in some examples, the probe axis 304 mayalso coincide with a transducer surface normal. FIG. 3 shows apositioning of the transducer probe 304 as used to acquire the 3Dultrasound data represented by the volume-rendered image.

Arrow 308 shows a radial direction which is defined as being parallel tothe probe axis 304. For example, when the radial direction 308 is theviewing direction, the user may be presented with a top-down view of thescanned object represented by the volume-rendered image.

The resolution of some ultrasound data may be anisotropic in nature. Forexample, the point spread function of the ultrasound imaging system(e.g., such as the ultrasound imaging system 100 shown in FIG. 1) may behighly asymmetric and thus the resolution of the resultingvolume-rendered image is different in the radial direction 308 versus alateral direction (as show by arrow 310) and an elevation direction (asshown by arrow 314). More specifically, the image resolution in theradial direction 308 is higher than in the lateral direction 310 and theelevation direction 314. As shown in FIG. 3, the lateral direction 310is perpendicular to the probe axis 304. Additionally, the elevationdirection 314 is perpendicular to the probe axis 304 (and radialdirection) and the lateral direction 310.

A user may adjust the viewing direction via a user interface (such asuser interface 115 shown in FIG. 1) by rotating the volume-renderedimage displayed on a display screen (such as display 118 shown in FIG.1). As the viewing direction changes from the radial direction 308 andmoves closer to the lateral direction 310, the resulting volume-renderedimage may become increasingly noisy and/or unstable due to theanisotropic nature of the 3D ultrasound data. In some examples, thevolume rendering parameters used in the volume rendering algorithm(e.g., including the volume-rendering shading parameters used to shadethe image and volume-rendering shadowing parameters used to shadow theimage), as described above, may result in different quality images fordifferent viewing directions relative to a same probe axis. As oneexample, when a 3D dataset of a tissue is viewed from the side (e.g.,lateral direction 310), the inherent speckle pattern in the data createssome shadows and reflections which do not correspond to real tissuestructures. As such, medical diagnosis based on the resultingvolume-rendered image may be less accurate.

Instead of applying the same shading and shadowing volume renderingparameters to all images, regardless of the viewing direction, at leastduring some selected conditions, a method may include adjusting therendering parameters based on the viewing direction of thevolume-rendered image relative to the probe axis 304. In other examples,the rendering may only be adjusted based on the viewing direction of thevolume-rendered image relative to the probe axis during selectedoperating or viewing conditions, and in other conditions the renderingmay be maintained independent of the viewing direction of thevolume-rendered image relative to the probe axis 304. FIG. 3 shows anangle, a, defined between the transducer probe axis 304 of thetransducer probe 306 and the viewing direction 312 of thevolume-rendered image 302. A weighting function based on a may then beused to adjust the rendering parameters and therefore adjust the amountof opacity and light reflections represented in the volume-renderedimage as a function of α. As one example, the weighting function isdefined as:

1−sin(α)*A  (equation 1),

where A is an angle dependency term. As one example, the angledependency term may be based on a known relationship between the viewingdirection and an image quality of the volume-rendered image. As such,the angle dependency term may be different for different imaging systemsand based on a point spread function of the imaging system (e.g.,ultrasound imaging system). The output of the weighting function is thenmultiplied with the light reflection term (e.g., which may include aspecular reflection term and/or a diffuse reflection term) as well asthe light attenuation term (e.g., opacity) in the volume renderingalgorithm. For example, when viewing the volume data from the transducerprobe position (e.g., from the radial direction 308), sin(α)=0 and thusthe weighting function is 1. As a result, the volume rendering shadingand shadowing parameters (also referred to herein as shading andshadowing parameters), such as the light reflection term and the lightattenuation term, are not adjusted and the volume-rendered image isshaded and shadowed according to the unadjusted parameters. However, asanother example, when viewing the volume data from the side, or from thelateral direction 310, sin(α)=1 and thus the weighting function is 1−A.As a result, the volume rendering parameters are adjusted by 1−A and theresulting volume-rendered image is shaded and shadowed according to theadjusted rendering parameters. In this way, the shading and shadowing ofthe volume-rendered image may be adjusted based on the viewing anglerelative to the transducer probe axis. By adjusting the shading andshadowing based on the angle α, the resolution of the volume-renderedimage is made more isotropic than if the shading was not adjusted basedon the angle α. Thus, adjusting the shading and shadowing based on theangle α produces more realistic volume-rendered images from any viewingangle and results in more accurate medical diagnosis from theangle-adjusted images.

FIG. 4 is a flow chart of a method 400 in accordance with an embodiment.According to exemplary embodiments, the method 400 may be performed withthe system 100 shown in FIG. 1. The technical effect of the method 400is the display of a volume-rendered image that is shaded and/or shadowedbased on a viewing direction of the volume-rendered image relative to aprobe axis of a transducer probe (as shown in FIG. 3) used to acquirethe three-dimensional (3D) data. FIG. 4 will be described according toan exemplary embodiment where the method 400 is performed with theultrasound imaging system 100 shown in FIG. 1. However, according toother embodiments, the method 400 may also be performed with otherultrasound imaging systems or with different medical imaging devices.Additionally, according to other embodiments, the method 400 may beperformed by a workstation that has access to 3D ultrasound data thatwas acquired by a separate ultrasound imaging system.

An ultrasound imaging system acquires a 3D medical imaging dataset(e.g., 3D ultrasound dataset) with a transducer probe and stores themedical imaging dataset in the memory of the system (such as memory 120shown in FIG. 1). The transducer probe is positioned on an objectsurface.

Method 400 begins at step 402, where the processor of the ultrasoundimaging system (such as processor 116 shown in FIG. 1) accesses a 3Dultrasound imaging dataset from a memory, such as the memory 120 shownin FIG. 1. In another embodiment, the 3D ultrasound data may be accessedin real-time as the data is acquired by the ultrasound probe (e.g., suchas probe 105 shown in FIG. 1). The 3D ultrasound dataset may includevoxel data where each voxel is assigned a value and an opacity. Thevalue and opacity may correspond to the intensity of the voxel. At 404,the processor generates a volume-rendered image from the 3D ultrasoundimaging dataset. According to an embodiment, the processor may generatethe volume-rendered image according to one of the techniques previouslydescribed with respect to FIG. 2. As part of the generation of thevolume-rendered image during 404, the processor determines (e.g.,calculates) the shading for the volume-rendered image. As describedhereinabove with respect to FIGS. 2-3, the shading of thevolume-rendered image may include calculating how light from one or moredistinct light sources would interact with the structures represented inthe volume-rendered image. The volume rendering algorithm controllingthe shading may calculate how the light would reflect, refract, anddiffuse based on intensities, opacities, and gradients in the 3Dultrasound imaging dataset. The intensities, opacities, and gradients inthe 3D ultrasound imaging dataset may correspond with tissues, organs,and structures in the volume-of-interest from which the 3D ultrasounddataset was acquired. As one example, at 404, the processor uses thelight from the one or more light sources in order to calculate theamount of light along each of the rays used to generate thevolume-rendered image. The positions, orientations, and other parametersassociated with the one or more lights sources will therefore directlyaffect the appearance of the volume-rendered image. In addition, thelight source(s) may be used to calculate shading with respect tosurfaces represented in the volume-rendered image. In one example, theshading may be adjusted based on a position of the light source relativeto the volume-rendered image.

As described above, shading and/or shadowing the volume-rendered imagemay include applying one or more of depth coloring, direct lighting,indirect lighting, ambient lighting, specular and diffuse reflections,and HDR processing to the volume-rendered image. Further, applyingshading and/or shadowing to the volume-rendered image at 404 may includecalculating shading of the volume-rendered image based on one or morevolume-rendering shading parameters. As one example, the one or morevolume-rendering shading and shadowing parameters may include a lightreflection parameter (e.g., such as a specular reflection parameter) anda light attenuation parameter, where the light reflection parameterdetermines an amount (e.g., strength) of shading and the lightattenuation parameter determines an amount (e.g., strength) of shadowingapplied to the volume-rendered image.

At 406, the method includes adjusting one or more of thevolume-rendering shading and shadowing parameters used to shade andshadow the volume-rendered image based on a viewing direction of thevolume-rendered image relative to the probe axis of the transducerprobe. As described above with reference to FIG. 3, the viewingdirection may be a direction in which a viewer (e.g., user) views thevolume-rendered image. For example, the viewer may view thevolume-rendered image from a radial direction (e.g., a directionparallel to the transducer probe axis, as applied to the tissuerepresented by the volume-rendered image), a lateral direction (e.g., adirection perpendicular to the transducer probe axis), an elevationdirection, or some other direction in between these directions. Anangle, α, is defined between the transducer probe axis (e.g., centralaxis of the transducer probe normal to the transducer surface, asdescribed above with regard to FIG. 3) and the viewing direction, asshown in FIG. 3. The angle α is then input into a weighting function forangle dependency, such as equation 1 described above with reference toFIG. 3. The output of the weighting function is then applied to thevolume rendering algorithm to adjust the volume rendering parameters.For example, the output of the weighting function may be applied to theone or more volume rendering parameters used to shade thevolume-rendered image, such as the light reflection parameter and thelight attenuation parameter (e.g., opacity). As another example, theoutput of the weight function may be applied to the light attenuationparameter (e.g., opacity) used to shade the volume-rendered image. As aresult, the shading and shadowing of the volume-rendered image isadjusted based on the angle α.

At 408, the processor displays the angle-dependent, shaded and shadowedvolume-rendered image on a display device (such as display device 118)of the ultrasound imaging system. At 410, the processor determines ifthe angle α has changed. For example, the processor may receive a signalfrom the user interface, indicating that a user has moved (e.g.,rotated) the volume-rendered image, thereby changing the viewingdirection of the volume-rendered image, and the angle α has changed. Forexample, the user may rotate the volume-rendered image from the radialdirection to the lateral direction in order to view the image from theside vs. a top view while the probe axis remains the same. As a result,the angle α increases. In another example, during an acquisition eventwhere a user may adjust a position of the transducer probe, the probeaxis may change, thereby changing the angle α. Thus, the angle α maychange responsive to the viewing direction and/or the probe axischanging.

If the processor has not received a signal indicating that the angle αhas changed, the method continues to 412 to maintain the currentvolume-rendering shading parameters used to shade the volume-renderedimage. Alternatively, if the angle α has changed, the method continuesto 414 where the processor adjusts the volume-rendering shading andshadowing parameters based on the newly received angle α (which isdifferent than the original angle). The method at 414 may follow asimilar method to that of 406. For example, the processor may update theweighting term based on the new angle α. The processor may then applythe updated weighting term to the one or more volume-rendering shadingparameters (e.g., the light reflection parameter and the lightattenuation parameter) and shadowing parameters (e.g. the lightattenuation parameter). At 416, the processor updates the shading of thevolume-rendered image based on the adjusted shading and shadowing volumerendering parameters. In one example, if the new angle α is greater thanthe previous angle α (e.g., the viewing direction has moved further fromthe radial direction and the probe axis), the amount of shading andshadowing of the volume-rendered image is reduced from thevolume-rendered image displayed at 408. Even if the probe axis stays thesame, if the viewing direction moves, then the angle α changes and theshading and shadowing are updated at 416. At 418, the processor displays(e.g., via a display device) the updated volume-rendered image havingthe updated shading and shadowing. In some examples, the adjusting andupdating at 414 and 416 may occur while a user is acquiring 3Dultrasound data with the transducer probe and the volume-rendered imagesmay be shaded, shadowed, and updated in real-time.

In different embodiments, only one of or both of shading and shadowingmay be used to generate the volume-rendered image. Thus, method 400 mayinclude applying and adjusting one or both of shading and shadowing tothe volume-rendered image. As one example, only shading and notshadowing may be applied to and used to generate the volume-renderedimage. As such, when the viewing angle changes, only the shadingparameters may be adjusted for the volume-rendered image. In anotherexample, only shadowing and not shading may be applied to thevolume-rendered image. Thus, when the viewing angle changes, only theshadowing parameters may be adjusted for generating the updatedvolume-rendered image. In yet another example, both shading andshadowing may be applied to generate the volume-rendered image. Thedetermination of whether to apply shading, shadowing, or both, to thevolume-rendered image may be based on different conditions (e.g., suchas the type of tissue acquired, the imaging system properties, thepreference of the user, the type of diagnostic being performed based onthe generated volume-rendered image, the viewing angle, etc.). Thus,there may be different conditions for applying shading, shadowing, orboth to the volume-rendered image. In one example, a user may selectwhich of the shading, shadowing, or both, are applied when generatingthe volume-rendered image. In this way, the shading and shadowing of thevolume-rendered image is independently enabled by the user. Further,different amount of shading and shadowing may be applied to the sameimage. For example, a user may select to apply a greater amount ofshading than shadowing to the volume-rendered image. In this way, thedegree of each of the shading and shadowing may be selected. Furtherstill, different parts (e.g., regions) of a single volume-rendered imageor different images in a time sequence of an acquisition event, may beshaded and shadowed differently (e.g. different amount of each ofshading and shadowing may be applied, or only one or the another may beapplied). In all cases, both the shading and shadowing are created andupdated based on the same angle between the probe axis of the transducerprobe and the viewing direction of the volume rendered image (e.g., a,as described above). For example, when both shading and shadowing areused to generate the volume-rendered image, both the shading andshadowing are based on the same angle between the probe axis and theviewing direction.

In this way, a volume-rendered image generated from a three-dimensionalultrasound dataset may be shaded and/or shadowed based on an anglebetween a probe axis of a transducer probe and a viewing direction ofthe volume-rendered image. For example, one or more volume-renderingshading and shadowing parameters used to calculate the shading and/orshadowing of the volume-rendered image may be adjusted based on thedetermined angle between the probe axis and the viewing direction. Asthe angle increases, an amount of shading and/or shadowing applied tothe volume-rendered image may be reduced, thereby increasing a qualityof the image resolution at different viewing directions. Since theresolution of the image is anisotropic, adjusting the shading and/orshadowing of the volume-rendered based on the angle between the probeaxis and the viewing direction reduces the noise and smoothens thevolume rendered image. As a result, more accurate medical diagnosis maybe made from any viewing direction of the volume-rendered image.

As one embodiment, a method for ultrasound imaging comprises generatinga volume-rendered image with shading and shadowing from athree-dimensional ultrasound dataset, the shading and shadowing based onan angle between a probe axis of a transducer probe used to acquire thethree-dimensional ultrasound dataset and a viewing direction of thevolume-rendered image. As one example, the shading and shadowing for thevolume-rendered image are determined based on a light source and one ormore volume-rendering shading and shadowing parameters, where the one ormore volume-rendering shading and shadowing parameters are adjustedbased on the angle. The method may further comprise adjusting the one ormore volume-rendering shading and shadowing parameters by multiplyingthe one or more volume-rendering shading and shadowing parameters by aweighting function, wherein the weighting function is a function of theangle, and wherein the weighting function decreases an amount of shadingand shadowing of the volume-rendered image as the angle increases. Inone example, the weighting function includes an angle dependency term.In another example, the one or more volume-rendering shading andshadowing parameters includes a light attenuation parameter thatdetermines a shade and shadow strength for the volume-rendered image anda light reflection parameter that determines an intensity of thereflected light. The method may further comprise determining an amountof shadowing and shading of the volume-rendered image based on theadjusted one or more volume-rendering shading and shadowing parametersand reducing the amount of shadowing and shading as the angle increases.The method may additionally comprise displaying the volume-renderedimage. As another example, in response to a change in the angle, themethod may include updating the shading and shadowing based on thechange in the angle and displaying the volume-rendered image with theupdated shading and shadowing. Additionally, the probe axis is a centralaxis of the transducer probe which is positioned normal to a planetangent to a surface formed by transducer elements of the transducerprobe.

As another embodiment, a method for ultrasound imaging comprisesgenerating a volume-rendered image with a first shading and a firstshadowing from a three-dimensional ultrasound dataset, the first shadingand the first shadowing based on an angle between a probe axis of atransducer probe used to acquire the three-dimensional ultrasounddataset and a viewing direction of the volume-rendered image; displayingthe generated volume-rendered image; and in response to a change in theangle, updating the volume-rendered image with a second shading and asecond shadowing, different than the first, the second shading and thesecond shadowing based on the change in the angle, and displaying theupdated volume-rendered image. In one example, generating thevolume-rendered image with the first shading and the first shadowingincludes calculating the first shading and the first shadowing for thevolume-rendered image based on one or more volume-rendering shadingparameters, where the one or more volume-rendering shading and shadowingparameters are adjusted based on the angle. The method may furthercomprise adjusting the one or more volume-rendering shading andshadowing parameters by multiplying the one or more volume-renderingshading and shadowing parameters by a weighting function, where theweighting function is a function of the angle and includes an angledependency term. Further, as one example, the one or morevolume-rendering shading and shadowing parameters that are adjustedbased on the angle include a light reflection parameter and a lightattenuation parameter. As another example, updating the volume-renderedimage with the second shading and the second shadowing includescalculating the second shading and the second shadowing based on one ormore volume-rendering shading and shadowing parameters, where the one ormore volume-rendering shading and shadowing parameters are adjustedbased on the change in the angle. The method may further comprise, inresponse to the angle increasing, adjusting the one or morevolume-rendering shading and shadowing parameters by a greater amountthan for the first shading and the first shadowing and decreasing anamount of shading and shadowing applied to the volume-rendered image. Inanother example, the method may further comprise, in response to theangle decreasing, adjusting the one or more volume-rendering shading andshadowing parameters by a smaller amount than for the first shading andthe first shadowing and increasing an amount of shading and shadowingapplied to the volume-rendered image. Additionally, as one example,resolution of the three-dimensional ultrasound dataset is anisotropic.

As yet another embodiment, an ultrasound imaging system having ananisotropic point spread function, comprises: a transducer probe adaptedto scan a volume of interest; a display device; a user interface; and aprocessor in electronic communication with the transducer probe, displaydevice, and user interface. The processor is configured to: generate avolume-rendered image from three-dimensional ultrasound data acquiredwith the transducer probe; apply one or more shading and shadowingparameters to the volume-rendered image; adjust the one or more shadingand shadowing parameters based on an angle between a probe axis of thetransducer probe and a viewing direction of the volume-rendered image;and display the volume-rendered image on the display device. As oneexample, the processor is further configured to adjust the one or moreshading and shadowing parameters by multiplying the one or more shadingand shadowing parameters by a weighting function, where the weightingfunction includes an angle dependency term and is a function of theangle. Additionally, the processor may be further configured to: receivea change in the viewing direction from the user interface; determine theangle based on the change in the viewing direction and a current probeaxis; and if the angle has changed, adjust the one or more shading andshadowing parameters based on the changed angle to update the shadingand shadowing of the volume-rendered image and display thevolume-rendered image on the display device with the updated shading.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty. The terms “including” and “in which” are used as theplain-language equivalents of the respective terms “comprising” and“wherein.” Moreover, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects.

The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby a processor of an imaging system in combination with the varioushardware of the imaging system, such as a transducer probe, userinterface, and display.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

1. A method for ultrasound imaging, comprising: generating avolume-rendered image with at least one of shading and shadowing from athree-dimensional ultrasound dataset, the shading and shadowing based onan angle between a probe axis of a transducer probe used to acquire thethree-dimensional ultrasound dataset and a viewing direction of thevolume-rendered image.
 2. The method of claim 1, wherein the at leastone of shading and shadowing for the volume-rendered image aredetermined based on a light source and one or more volume-renderingshading and shadowing parameters, where the one or more volume-renderingshading and shadowing parameters are adjusted based on the angle.
 3. Themethod of claim 2, further comprising adjusting the one or morevolume-rendering shading and shadowing parameters by multiplying the oneor more volume-rendering shading and shadowing parameters by a weightingfunction, wherein the weighting function is a function of the angle, andwherein the weighting function decreases an amount of shading andshadowing of the volume-rendered image as the angle increases.
 4. Themethod of claim 3, wherein the weighting function includes an angledependency term.
 5. The method of claim 3, wherein the one or morevolume-rendering shading and shadowing parameters includes a lightattenuation parameter that determines a shadow strength for thevolume-rendered image and a reflection parameter that determines anintensity of the reflected light.
 6. The method of claim 2, furthercomprising determining an amount of the at least one of the shadowingand shading of the volume-rendered image based on the adjusted one ormore volume-rendering shading and shadowing parameters and furthercomprising reducing the amount of the at least one of the shadowing andshading as the angle increases.
 7. The method of claim 1, furthercomprising generating the volume-rendered image with both shading andshadowing and displaying the volume-rendered image, wherein the shadingand shadowing includes surface light attenuation and surface lightreflectivity in the displayed image.
 8. The method of claim 7, furthercomprising in response to a change in the angle, updating the shadingand shadowing based on the change in the angle and displaying thevolume-rendered image with the updated shading and shadowing.
 9. Themethod of claim 1, wherein the probe axis is a central axis of thetransducer probe which is positioned normal to a plane tangent to asurface formed by transducer elements of the transducer probe.
 10. Amethod for ultrasound imaging, comprising: generating a volume-renderedimage with at least one of a first shading and a first shadowing from athree-dimensional ultrasound dataset, the at least one of the firstshading and the first shadowing based on an angle between a probe axisof a transducer probe used to acquire the three-dimensional ultrasounddataset and a viewing direction of the volume-rendered image; displayingthe generated volume-rendered image; and in response to a change in theangle, updating the volume-rendered image with at least one of a secondshading and a second shadowing, different than the first, the at leastone of the second shading and the second shadowing based on the changein the angle, and displaying the updated volume-rendered image.
 11. Themethod of claim 10, wherein generating the volume-rendered image withthe at least one of the first shading and the first shadowing includescalculating the at least one of the first shading and the firstshadowing for the volume-rendered image based on one or morevolume-rendering shading and shadowing parameters, where the one or morevolume-rendering shading and shadowing parameters are adjusted based onthe angle.
 12. The method of claim 11, further comprising adjusting theone or more volume-rendering shading and shadowing parameters bymultiplying the one or more volume-rendering shading and shadowingparameters by a weighting function, wherein the weighting function is afunction of the angle and includes an angle dependency term.
 13. Themethod of claim 11, wherein the one or more volume-rendering shading andshadowing parameters that are adjusted based on the angle include one ormore of a light reflection parameter and a light attenuation parameter.14. The method of claim 10, wherein updating the volume-rendered imagewith the at least one of the second shading and the second shadowingincludes calculating at least one of the second shading and the secondshadowing based on one or more volume-rendering shading parameters,where the one or more volume-rendering shading and shadowing parametersare adjusted based on the change in the angle.
 15. The method of claim14, further comprising: in response to the angle increasing, adjustingthe one or more volume-rendering shading and shadowing parameters by agreater amount than for the at least one of the first shading and firstshadowing and decreasing an amount of shading and shadowing applied tothe volume-rendered image; and in response to the angle decreasing,adjusting the one or more volume-rendering shading and shadowingparameters by a smaller amount than for the at least one of the firstshading and the first shadowing and increasing an amount of shading andshadowing applied to the volume-rendered image.
 16. The method of claim1, further comprising generating the volume-rendered image with both thefirst shading and the first shadowing, where both the first shading andfirst shadowing are based on the angle, and in response to the change inthe angle, updating the volume-rendered image with both the secondshading and the second shadowing, where both the second shading and thesecond shadowing is based on the change in the angle.
 17. The method ofclaim 10, wherein the three-dimensional ultrasound dataset isanisotropic and wherein the shading includes light reflection and theshadowing includes light attenuation.
 18. An ultrasound imaging systemhaving an anisotropic point spread function, comprising: a transducerprobe adapted to scan a volume of interest; a display device; a userinterface; and a processor in electronic communication with thetransducer probe, display device, and user interface, where theprocessor is configured to: generate a volume-rendered image fromthree-dimensional ultrasound data acquired with the transducer probe;apply one or more shading and shadowing parameters to thevolume-rendered image; adjust the one or more shading and shadowingparameters based on an angle between a probe axis of the transducerprobe and a viewing direction of the volume-rendered image; and displaythe volume-rendered image on the display device.
 19. The system of claim18, wherein the processor is further configured to adjust the one ormore shading and shadowing parameters by multiplying the one or moreshading and shadowing parameters by a weighting function, where theweighting function includes an angle dependency term and is a functionof the angle.
 20. The system of claim 18, wherein the processor isfurther configured to: receive a change in the viewing direction fromthe user interface; determine the angle based on the change in theviewing direction and a current probe axis; and if the angle haschanged, adjust the one or more shading and shadowing parameters basedon the changed angle to update the shading and shadowing of thevolume-rendered image and display the volume-rendered image on thedisplay device with the updated shading and shadowing.